Variations in fastener design have been used to improve different characteristics and performance of fasteners depending on the intended use of the fastener. In general, a screw-type fastener includes a threaded shank with a pointed tip at one end thereof and a head at the other end. The head has a recess or other connector to accept a driving tool tip.
Fastener design can vary based on whether the design is used as a self-drilling fastener, or used with a pre-drilled bore, and based on the type of material for which the fastener is to be used. One type of material for which specialized fasteners provide advantages are low density materials, such as cellular PVC (polyvinyl chloride). Cellular PVC is a solid, extruded material that has the working characteristics of wood, and is used for interior trim, exterior trim, and paneling as well as windows and doors, blinds, and furniture.
Low density materials present issues with fastener pull-down and so-called pig-tailing, where portions of the material are extruded by the movement of the fastener into the material. The material extruded by the fastener takes the shape of a pig-tail which must thereafter be removed to provide a finished work.